Autunite and meta-autunite are radioactive, yellowish to yellowish-green, uranium-bearing minerals.  They are both hydrous calcium uranyl phosphate minerals - autunite is Ca(UO2)2(PO4)211H2O and meta-autunite is Ca(UO2)2(PO4)26-8H2O.


Autunite is an alteration product of other uranium minerals and typically occurs in hydrothermal veins and pegmatitic granites.  It has a nonmetallic, glassy to pearly luster, varies from pale yellow to yellow to greenish yellow to pale green to dark green to greenish black, has a yellowish streak, is soft (H=2 to 2.5), and has 3 cleavage planes, one of which is perfect (micaceous) and two of which are poor.  Autunite crystals are tabular in shape, having squarish to rectangular to 8-sided outlines, and range from transparent to translucent to opaque.  Many autunite specimens are finely-crystalline aggregates or microcrystalline crusts.  Thin crystals and thin cleavage fragments are flexible (elastic).  Autunite fluoresces under ultraviolet (UV) light.


Meta-autunite is a more stable, partial-dehydration product of autunite, and many "autunite" specimens are likely meta-autunite.  Meta-autunite has a nonmetallic, glassy to pearly to dull luster, a bright yellow to greenish yellow color, yellowish streak, is soft (H=2 to 2.5), and has one perfect cleavage (micaceous).  Unlike autunite, thin crystals and cleavage fragments of meta-autunite are brittle, not flexible.  Meta-autunite crystals are tabular squares to pseudocubes to pseudomorphs of autunite.  Finely-crystalline to microcrystalline crusts are common.  Meta-autunite is also fluorescent under UV light.


Autunite (above & below) from Autun, France (Colorado School of Mines Geology Museum public display, Golden, Colorado, USA). 



Meta-autunite from Margnac, Limousin, France (CSM # 69.145, Colorado School of Mines Geology Museum, Golden, Colorado, USA).



Photo gallery of autunite

Photo gallery of meta-autunite



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